Video compression may be desirable for reducing the required video storage space and for reducing the bandwidth for transmission of digital video data. For example, modem video surveillance systems may require large amounts of memory storage space for recording video captured by a large amount of cameras for long time periods. Video compression may also be desirable for streaming video, as it is known in the art, where video content is distributed over a computer network, for example, for use in an Internet Protocol Television (IPTV) system.
Some video encoding formats, including but not limited to, for example, H.263, H.264, MPEG-4 part 2, MPEG-4 part 10, and the like, include two principal types of compressed frames, or slices: independent frames, known as INTRA frames (or I-frames), and dependent frames, known as “INTER” frames. I-frames are compressed independently, irrespective of other frames, while INTER frames may record only the differentiating data between frames. Thus, the original video data may be reconstructed independently from an I-frame, making it the starting point for the decoding process. However, the achievable compression ratio for an I-frame is typically lower than the compression ratio for INTER frame, and thus, I-frames usually require larger storage space than INTRA frames. For example, video from surveillance systems usually has a spatially high temporal redundancy level, because it may typically overview a static scene with motion a small portion of the frame, e.g., less than 20% of the frame.
The distance between two consecutive I-frames is called INTRA cycle (IC). One method of reducing the storage space required for recording video and to reduce the bandwidth required to transport compressed video streams is to increase the IC. For example, MPEG-2 and MPEG-4 part 10 allow large IC, e.g., one I-frame every five seconds. However, as the receiving decoder may need to wait for an I-frame before displaying a complete image, an increase in IC may translate into longer frame reconstruction times. Additionally, small IC allows substantially random access to the video sequence. In video networking, small IC may improve overall video quality as I-frames end the accumulation of errors in the video sequence.
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